Field of the Invention
The present invention is generally directed toward a composite material comprising graphene or reduced graphene oxide and a polymer-derived ceramic material. The composite materials according to the present invention can be used to construct anodes, which can be used in batteries, particularly lithium ion batteries.
Description of the Prior Art
Rechargeable lithium ion batteries (LIBs) have been in use since the early 1990s for the powering of portable electronic devices that required low self-discharge, less maintenance, high operating voltage and high-energy density. However, the growing popularity of LIBs in the area of battery powered vehicles, intermittent storage in power grids and aerospace applications have gradually pushed the LIB operating requirements to higher cyclic efficiency, high power density, high specific capacity, and sustained capacity at higher cycling rates. The capacity of a LIB is theoretically limited by the electrode materials used. Typically, the anode and cathode are graphite (˜372 mAhg−1) and LiCoO2 (˜140 mAhg−1). To date, the most commonly used anode material in LIBs is graphite due to its stable cycleability, high coulombic efficiency, and structural stability. But the drawbacks such as low reversible capacity and poor capacity retention at higher operating current densities have fueled the research of designing an anode material superior to graphite.
To this end, certain silicon-containing composite anodes have shown great promise. Recent research has shown considerable improvements in cycling performance for Si-coated carbon nanotubes, thin films, Si/C core/shell composites, and polymer-derived SiOC ceramics for negative electrodes. Of various silicon-based anode architectures, polymer-derived SiOC is perhaps the most unique and the least studied anode material in this class. SiOC is a high temperature glass-ceramic with an open polymer-like network structure consisting of mixed bonds of Si with 0 and C atoms. This ceramic has a weight density of 2.1 g/cc, which is two thirds that of SiC or SiO2 crystalline phases. This open structure enables high charge and discharge rates with higher gravimetric capacity than graphite. However, much like other anode materials, SiOC anode preparation involves mixing with conducting agents and binders (ratio 8:1:1), followed by slurry coating on a Cu current collector foil before use as a battery electrode.
In this context, the graphene-based multi-component composite anodes are an attractive alternative primarily because of larger interlayer spacing in restacked graphene, high surface area, high electronic conductivity, and its ability to be readily interfaced with lithium active redox components, such as germanium/silicon nanoparticles or transition metal oxides like MoS2, SnO2, TiO2, and Fe3O4, to generate anodes that are inherently conducting, mechanically robust, and exhibiting high lithium intercalation capacity and rate capability. These porous anodes offer advantages over the traditional anodes in terms their ability to accommodate large strains associated with continued Li cycling and elimination of the dead weight of copper current collector, which accounts for approximately 10% of the total battery weight. Weight of the battery anode can be further reduced by another 20% by elimination of non-active phases such as polymeric binders and conducting agents.
However, the aforementioned graphene paper-based anodes do not offer a complete solution. They are either (a) too thin (sub-micron), which may limit the overall battery capacity due to insufficient active mass, or (b) require expensive synthesis techniques. More importantly, these anodes generally show very high first cycle loss (as much as 50%), low cycling efficiency (95 to 98%) and also poor capacity retention at high current densities (damage at high C-rates), making them impractical for use in a Li-ion battery fuel cell.